Production of sialon

Abstract

A process is described for preparing β'-sialon comprising heating a mixture of particles comprising from 70% to 90% by weight of particles of an aluminosilicate material and from 30% to 10% by weight of particles of a carbonaceous material at a temperature in the range of from 1300° C. to 1600° C. in nitrogen in a vessel in a manner such that the particles are in substantially continuous motion relative to each other and relative to the nitrogen. The residence time of the particles in the vessel does not exceed 3 hours.

I claim: 
     
       1. A process for preparing β'-sialon, which process comprises heating a mixture of particles comprising from 70% to 90% by weight of particles of an aluminosilicate material and from 30% to 10% by weight of particles of a carbonaceous material at a temperature in the range of from 1300° C. to 1600° C. in nitrogen in a reaction vessel and causing said particles to be in substantially continuous motion relative to each other and relative to the nitrogen and wherein the residence time of the particles in the reaction vessel does not exceed three hours, and wherein the aluminosilicate material comprises a kandite clay which has been calcined at a temperature of from 450° C. to 1300° C. such that loss on ignition of the calcined clay at 1000° C. for 2 hours is not more than 1% by weight. 
     
     
       2. A process according to claim 1, wherein the mixture of particles comprises from 75% to 85% by weight of particles of the aluminosilicate material and wherein the mixture of particles comprises from 25% to 15% by weight of particles of the carbonaceous material. 
     
     
       3. A process according to claim 1 wherein the carbonaceous material comprises finely divided carbon or carbon black. 
     
     
       4. A process according to claim 3 and further comprising the step of comminuting the carbonaceous material to a particle size distribution such that at least 20% by weight of the carbon consists of particles having an equivalent spherical diameter of less than 2 μm, the comminuting step being carried out before mixing the carbon with the aluminosilicate material. 
     
     
       5. A process according to claim 1 and wherein the process is carried out in an enclosed furnace. 
     
     
       6. A process according to claim 5 and wherein the enclosed furnace comprises a rotary furnace having a longitudinal axis about which it rotates. 
     
     
       7. A process according to claim 5 and wherein the enclosed furnace comprises a fluidised bed. 
     
     
       8. A process as claimed in claim 1 and wherein the mixture of particles comprises granules comprising the aluminosilicate and carbonaceous materials and wherein the average size of the granules is in the range 0.2 mm to 5.00 mm. 
     
     
       9. A process claimed in claim 8 and wherein the granules comprise metakandite and finely divided carbon. 
     
     
       10. A process as claimed in claim 8 further comprising producing the mixture of particles by preparing a first aqueous slurry comprising particles of the aluminosilicate material and a second aqueous slurry comprising particles of the carbonaceous material and combining said first slurry and said second slurry to form a slurry mixture; drying the slurry mixture; and pelletizing the mixture to form the granules. 
     
     
       11. A process as claimed in claim 5 and wherein the reaction vessel comprises a single stage zone at which the sialon producing reaction is carried out. 
     
     
       12. A process as claimed in claim 5 sand wherein the reaction vessel comprises two or more zones in which different treatments of the mixture are carried out in series. 
     
     
       13. A process as claimed in claim 5 and wherein the reaction vessel comprises a fluidised bed. 
     
     
       14. A process according to claim 1 wherein the rate at which the nitrogen is supplied, in liters per minute, is at least 35 times the rate at which the mixture is supplied in kg per hour. 
     
     
       15. A process according to claim 1 wherein the residence time is from 30 minutes to 2 hours. 
     
     
       16. A process as claimed in claim 1 and wherein the mixture is fed to the reaction vessel and the β'-sialon is thereby produced in a substantially continuous manner. 
     
     
       17. A β'-sialon which is a product of the process claimed in claim 1. 
     
     
       18. A process according to claim 1 and wherein said substantially continuous motion of said particles relative to each other and relative to the nitrogen is a vigorous, agitated particle motion caused by said reaction vessel.